The housing or body configuration of a telephone line test set currently employed by telephone craftspersons is generally configured as diagrammatically illustrated at 1 in FIGS. 1 and 2 to include a first, generally hand and face-conformal case segment 10 containing earpiece and mouthpiece transducers, a second, keypad case segment 20, which houses a test set keypad and fits on a first back portion 21 of the case segment 10, and a third, clip case segment 30, which houses a belt clip 40 and fits on a second back portion 31 of the case segment 10, contiguous with the first back portion 21.
The first case segment 10 has a first flared body end 11, which is sized and shaped to accommodate an acousto-electrical transmitter unit (mouthpiece) 13. This first flared body portion 11 is connected by a second, central handle portion 15 which, in turn, adjoins a third flared body end 17, that is configured to accommodate a receiver-mounting structure, in which an electrical-to-acoustic receiver unit (earpiece) 19 is supported. Associated with the respective transmitter and receiver transducers are circuit components, typically mounted on printed circuit boards, that are arranged within the confines of the first case segment 10. The printed circuit boards are connected via a ribbon cable 23 at an upper end 24 of the keypad case segment 20 to a keypad unit 25, shown in dotted lines in FIG. 1 and in detail in FIGS. 3A, 3B and 3C (to be described).
Although the test set body is customarily formed of durable plastic material, the interior of the first case segment 10, where the printed circuit components reside, is usually vented to the atmosphere, so that contaminants (e.g. moisture and dust) are allowed to enter the case and are a source of potential degradation of the operation of the circuit components housed within the test set. Efforts to circumvent this contaminant-based degradation problem have included coating printed circuit assemblies with non-conductive passivating materials, coating the electrical contacts of individual components with non-conductive adhesives, and enclosing the printed circuit assemblies within a permanently sealed module. Unfortunately, these previous proposals have proven to be less than satisfactory.
More particularly, it has been found that coating the printed circuit assemblies is inadequate, since during the coating process, the coating material tends to pull away from the sharp points at the ends of the electrical contacts of circuit components, which leaves them exposed to contamination. Coating the electrical contacts has been not been found to provide consistently robust protection, due to inconsistencies in the coating application process, so that contaminants are not completely sealed out. Finally, placing the printed circuit assemblies inside a permanently sealed enclosure prevents repairs or retrofits without destroying the seal, which cannot be restored.